The present invention relates to the gathering of fibrous material in the form of a sliver or thin strand produced in the preparation of raw fibres for spinning, typically by cards or drawing frames set downstream of the carding operation. In the above processes of preparation of the raw fibres, the fibrous material in staple is opened in the form of individual fibres and set in parallel strands, any impurities or dirt that might be present are eliminated to a large extent, the fibres undergo a mixing or blending together, and a sliver of fibres is formed, which is gathered in large cans, then to be sent on to the subsequent stages of the process. In order to highlight the advantages and characteristics of the present invention, in what follows reference will be made to the sliver coming from a card of a cotton type, at the same time it being clearly emphasized that the invention may be applied also to slivers of different origin.
The operation of unloading, drawing and gathering the sliver produced on cards of a cotton type forms the subject of numerous patent applications in the name of the present applicant, for example the European patent applications EP-A-967 169, EP-A-1 001 058, EP-A-1 001 059, EP-A-1 022 365, to which the reader is referred for further details on the state of the art.
In particular, the subject of the present invention is the operation of gathering the sliver produced and the packaging thereof in the gathering can, and, in particular, modulated gathering thereof according to the requirements of the user of the sliver produced. Gathering of the sliver into cans renders the operations of carding upstream independent of the subsequent processes where the sliver is received.
FIG. 1 illustrates a conventional scheme for gathering the sliver into a can. From the card assembly 1 singularized and mixed fibres are obtained, which are gathered into a web and reduced to a sliver by a condenser. According to the patent applications referred to above, prior to delivery to the packaging device, the sliver is worked in a drawing assembly 2, which follows the condenser. In the gathering assembly the sliver 3 is recalled by the card assembly with two calenders (not shown in the figure) and set in overlapping coils in a cylindrical can 4 set underneath a rotating distributor 5. The said distributor is eccentric with respect to its supporting plate 6, which is above the filling can 4 and is driven according to two rotary motions: by a motion of revolution about its own center in the direction indicated by the arrow B, at a speed of the order of hundreds of revolutions per minute, and by a motion of rotation about the center of the plate 6 as indicated by the arrow C, at a much lower speed. The two combined rotations distribute the sliver 3 in the can 4 in coils, which translate their center according to circles that are coaxial with the plate 6, with an accumulation that progressively grows in thickness but not in level, as will be described in what follows.
At output from the card 1, on the path of the sliver 3 directed towards the gathering assembly 7 there are located the guide pulleys 8a, 8b and 8c in order to support it and reduce its free portion. In a position corresponding to one of the guide pulleys there is generally set a sensor, which detects the continuity of the sliver or any interruption of the sliver. In the latter case, the sensor in turn brings about stoppage of the machine. The main problems derive from the fact that the sliver produced in carding has a limited tensile strength and must be worked with all due caution. For this reason, the packaging in cans with overlapping coils enables the sliver to be subsequently taken out without generating any tensile forces that the limited strength of the sliver may not be able to withstand. For this purpose, in general the can 4 for gathering the sliver 3 is equipped with a mobile bottom 9, which is pushed upwards by an elastic element 10, for example a spring, which enables the bottom 9 to drop down accordingly as the process of depositing of the coils of sliver on its bottom progresses. With the above solution the free portion of sliver 3, from the distributor element 5 to the level at which the sliver is deposited remains extremely short. Both in the operation of gathering the sliver and in the subsequent operation, in which the sliver is taken from the can, the tensile stress exerted on the sliver is kept under control, and also a substantial effect of uncontrolled false drawing is prevented. In FIG. 1 are illustrated three cans 4, from left to right. The can 4 furthest to the left is an empty can, with its bottom 9 at the highest level. The initial depositing of sliver will take place with a free portion that corresponds to the limited difference in level that separates it from the crown or top of the plate 6, i.e., from the crown of the structure 15 which supports it. The can 4 in the middle is in the process of being filled, with its bottom 9 at an intermediate level. The can 4 furthest to the right is a full can, with its bottom 9 depressed to the minimum level by the winding of sliver deposited thereon. The cans are in general provided with wheels or balls for their movement on the treading surface. Alternatively, they may be displaced with auxiliary means, such as roller conveyors, trucks, and so forth.
The sliver produced by the card or by drawing frames set downstream of the card may have various destinations, which can basically be divided into two types. One type is that of the slivers destined to conventional spinning processes, which are to be sent onto subsequent drawing frames, for combing and then to ring spinning-machines. The gathering device 7 must then work for packaging the sliver in cans 4 of large diameter. The other type is that for uses which require smaller cans 4 and in general slivers with finer counts, for example open-end spinning. In the European patent application EP-A-342 116 there is described a device for gathering card sliver, which can operate in a single station with cans of different diameter, adapting the geometry of its members thereto.
As a rule in the textile industry the most widespread dimensions of cans are, generally speaking, a diameter of 18xe2x80x3 for the small can and a diameter of 40xe2x80x3 for the large can. Consequently, the process of gathering the sliver into two types of can takes place at different speeds of rotation and recall, also depending upon the tensile strength of the sliver, which varies according to the cases but which is always extremely small. Generally speaking, the gathering device for a given can size is not satisfactory for cans of another size both on account of problems of encumbrance and overall dimensions and according to the winding parameters involved.
In both types of gathering it is necessary for the linear speed of recall of the sliver 3 coming from the carding unit 1 by means of the calenders of the gathering unit 7 to correspond to the linear speed, to the speed of revolution B of the distributor 5, as well as to the depositing of the coils of sliver on the toroidal winding body inside the can; otherwise, the said depositing would not come about in a controlled way and according to the pattern described. The slow speed of rotation of the plate 6 about its center C is instead determined according to the number of turns of sliver that are to be deposited for each rotation of the plate and does not strictly depend upon the previous ones.
The above scheme for gathering the card sliver into a can presents certain drawbacks, which are more evident for gathering sliver into cans of larger size. A first drawback is identified in the complication, cost and encumbrance of the transmission for driving the plate 6, which must be set at the latter""s periphery, in order to allow for passage of the sliver being gathered, which is deposited by the rotating distributor. Another problem derives from the fact that the point of arrival of the sliver 3 from the last return motion of the pulley 8c is positioned on the vertical line passing through the center of the plate 6 for reasons of symmetry. Consequently, the length of the path between the last return motion of the pulley 8c and the calender for recall inside the distributor 5 varies at each rotation of the distributor according to a sinusoidal pattern between a minimum length, when the hole 12 for entry of the sliver into the distributor 5 is close to the center of the plate 6, and a maximum length, when the hole 12 for entry of the sliver into the distributor 5 is further away from the center of the plate 6. This variation in length causes a pulsating tensioning, which may induce an undesired pull on the sliver.
The present invention relates to a device for gathering card sliver into cans of different dimensions and according to procedures adapted to their size which enables the drawbacks described above to be overcome.